Powdered coal burning system



March 9, 1937.

L. L. KUEMPEL POWDERED COAL BURNING SYSTEM Filed Oct. 11, 19 54 tow Le on L.Kuempel Patented Mar. 9, 1937 UNITED "STATES PATENT OFFICE rowmzrmn COAL BURNING SYSTEM Application October 11, 1934, Serial No. 747,897

20 Claims.

The present invention relates to an improved detailed description and accompanying single control system for controlling the ignition and burning of fuel and is particularly directed to apparatus for burning finely divided solid fuel 5 such as powdered coal.

One of the objects of the present invention is r x the provision of a burner/control system in which a damper, such as a stack damper, that has a starting position and at least one running posi- 10 tion must be moved to such starting position before fuel can be initially supplied to the burner.

A further object of the invention is the provision of a variable fuel feeding system in which the fuel feed is normally varied so as to provide 15 a plurality of fuel feed rates upon changes in the demand for fuel and in which the fuel feed controlling means must be moved to a predetermined fuel feeding position before the fuel delivery means may be placed in operation after 20 which the fuel feed controlling means is controlled in accordance with the demands.-

A further object of the invention is the provision of a burner control system in which a draft control means or stack damper must be moved 25 to starting position and the fuel 'feed volume controlling means must be operated so as to permit a relatively small volume of fuel to be fed to the burner before the fuel feeding means can be placed in operation. 7

Further objects of the invention include the provision of systems of the type above described in which initiation of fuel feed to the burner is dependent upon the proper operation of an ignition means which is preferably of the flame pro- 35 ducing type.

Another object of the invention is the provision of systems of the nature set out above wherein operation of the ignition means is terminated after a timed period together with provision for maintaining operation of the fuel feed means in the event combustion has been properly established during the time that the ignition means was in operation. Preferably, a single means is utilized to respond to proper operation of the 45 ignition means, so as to permit the initial supplying of fuel, and to the main burner flame to maintain the supply of fuel to the burner after operation of the ignition means is terminated.

Other objects of the invention'reside in the 50 various combinations and sub-combinations to be hereinafter disclosed'and will be found in the drawing, the accompanying description and the appended claims.

For a more complete understanding of the in- 55 venticn, reference may be had to the following drawing which is a diagrammatic showing of one form of the invention.

Referring to the single figure of the drawing, it will be noted that the control system of the pres- 5 ent invention is entirely electrical, power being furnished by a hot line 5 and a ground line 6, there being a manually operable switch 1 interposed in these lines by which the circuit to the control system may be manually completed or interrupted. For convenience of illustration, the ground line 6 is shown connected. to ground at 8 and, throughout the description of the electrical circuits, the return lines from all of the various instruments and devices will be shown as connected to a similar ground 8.

The invention is shown as applied to a boiler ID that includes a stack or chimney H which is provided with a stack damper 12. The boiler I0 is fired by powdered coal' which is supplied thereto by a combined pulverizing and feeding mechanism generally indicated at l3. This pulverizing and feeding mechanism includes a motor It which drives a blower l5 and a pulverizer that is located in a casing l6. Coal is fed to the pulverizer by means of a hopper l'l. When the motor M is energized, the pulverizer in casing l6 is operated and the blower l5 operatesto suck the pulverized coal through a classifier l8 which only allows coal particles of the proper smallness to pass therethrough, after which the pulverized coal is drawn through a duct l9, passes through the blower I5 and is discharged to the boiler Ill through a discharge duct 20. For conveniencev of illustration, the duct 20 is shown broken away. In this manner, operation of the motor It serves to deliver a combination of powdered coal and combustion supporting air to the boiler In. The duct I9 is provided with a damper 2| of the butterfly type which is operative to vary the amount 0 v of fuel and air'delivered to the boiler I 0 and thereby vary the rate of combustion. Such combination pulverizers and fuel feeders are well known in the art and do not constitute a part of the present invention except in combination with the control system now to be described.

The fuel control damper 2| is controlled by a motor mechanism generally indicated at 25. This motor mechanism 25 is of the modulating or proportioning type as will hereinafter become apparent and includes a main control shaft 26 to which is secured a crank 27. The crank 27 is 1 connected to a similar crank 28 by means of a link 29, the crank 28 being in turn connected to the fuel control damper or valve 2i. The main operating shaft 26 further carries a gear 38 .and forth across a balancing resistance 58 which is operatively connected to a rotor shaft 3| through suitable gear reducing mechanism 32. The rotor shaft 3| carries a pair of motor rotors 33 and 34 which are respectively provided with energizing or field windings 35 and 36. The field windings 35 and 36 are controlled by a relay that includes a pair of similar relay windings 31 and 38 which conjointly control the position of the plunger 39. The plunger 39 is connected to a relay switch arm 48 by means of a non-magnetic and non-conducting connecting link 4|, the relay switch arm 48 being adapted to alternately engage a pair of relay contacts 42 and 43 upon reverse movements of the plunger 39. Relay coils 31 and 38 are controlled by a balanced solenoid mechanism which includes a pair of similar solenoid windings 45 and 46 which cooperate in the control of a single plunger 41. The plunger 41 is connected to a switch arm 48 by means of a non-magnetic and non-conducting link 49. The switch arm 48 is adapted to alternately engage a pair of contacts 58 and 5|. During the normal operation of the system, the energizations of solenoid windings 45 and 46 are controlled by a pressure-operated variable resistance means herein shown as comprising a pressure-operated potentiometer that includes a control resistance 53 and a cooperating contact arm 54 that is controlled by a pressure-responsive device herein shown as a bellows 55. The bellows 55 is connected to the boiler I8 by a pipe 56, which is shown broken away for convenience of illustration, whereby the contact arm 54 is positioned upon the control resistance 53 in accordance with variations in boiler pressure. The main operating shaft 26 further operates a balancing contact arm 51 that is moved by the main shaft 26 back The arrangement is such that the main shaft 26 has an extreme movement of one quarter of a revo lutionor whereby to position fuel control damper 2| between its open and closed positions by the linkage mechanism previously described. Electrical power is supplied to the motor mechanism 25 by means of line wires 68 and 6| which are connected to the primary 62 of a step down transformer 63, having a low voltage secondary 64. A wire 65 connects line wire 68 to the relay switch arm 48 and a wire 66 connects the line wire'6I to one end of each of field windings 35 and 36. The other end of field winding 35 is connected to relay contact 43 by a wire 61 and, in a like manner, the other end of field winding 36 is connected to relay contact 42 by means of a wire 68. The relay windings 31 and 38, in series, are connected across the secondary 64 of transformer 63 by means of wires 69, 10, 1|, and 12. Similarly, the solenoid windings 45 and 46, in series, are connected across the secondary 64 by wires 69, 13, 1|, and 14. The control resistance 53 and the balancing resistance 58, in parallel, are connected in parallel with the series connected solenoid windings 45 and 46 through two identical protective resistances 15 and 16 by means of wires 11, 18, 19, 88, 8|, and 82.

Motor mechanism 25 is additionally controlled by a pair of relays generally indicated at 85 and 86. The relay 85 includes a relay coil 81 that operates an armature 88 which in turn controls a pair of switch arms 89 and 98. The switch arms 89 and 98 are normally respectively engaged with contacts 9| and 92 but are moved into'respective engagement with contacts 93 and 94 upon energization of relay coil 81. The relay 86 comprises a relay coil 95 and a cooperating armature 96 that controls a single switch arm 91. The switch arm 91 normally engages a contact 98 but is moved from engagement therewith and into engagement with a contact 99 on energization of the relay coil 95.

The junction of solenoid windings 45 and 46, the balancing contact finger 51, and the switch arm 91 of relay 86 are all interconnected by means of wires I88, |8|, and |82. The control contact arm 54 is connected to the contact 93 of relay 85 by means of a wire I83. One end of control resistance 53 is connected to contact 98 of relay 86 by a wire I 84 and the other end thereof is connected to contact 9| of relay 85', through a manually operable rheostat I85 by means of wires I86 and I81. The junction of relay windings 31 and 38 are connected to switch arm 48 through a protective resistance I88 by means of wires I89 and 8. Contact 58 is connected to a small number of turns of solenoid winding 45 by means of a wire I and a wire 2 connects a small number of turns of the solenoid winding 46 to contact 5|.

The stack damper I2 for the boiler I8 is controlled by a motor mechanism generally indicatd at I28. This motor mechanism I28 includes a main shaft I2I to which a crank I22 is secured.

The crank I22 operates a link I23 that is connected to a gear segment I24 pivoted as at I25. The gear segment I24 meshes with a pinion I26 that is in turn secured to the shaft I21 of the stack damper I2. The main operating shaft I2I carries a gear I28 that is connected to a motor pinion I29 through suitable reduction gearing I38. The motor pinion I29 is carried by a rotor shaft I3| to which is secured a rotor I32. Associated with the rotor I32 is an energizing or field winding I33. The main operating shaft I2I also controls a rotary switching mechanism that includes a substantially circular track I34 with which a pair of contact buttons I35 and I36 are associated. The contact buttons I35 and I36 are diametrical opposite one another and lie in the arc of curvature of. the circular portions of track I34. A rotary brush I31 is controlled by main operating shaft I2| and is adapted to be constantly engaged with the track I34 or one of the buttons I 35 or I36, the arrangement being such that the brush I31 can rest upon either of buttons I 35 or I 36 and be completely out of engagement with the track I34. Main operating shaft I2I also carries a cam I 38 that is provided with an operating portion I39 that is adapted to depress a cam follower I48 which is normally urged upwardly by means of a spring MI. The

cam follower I48 carries a contact I42 that is moved into engagement with a cooperating contact I43 when the cam follower I48 is depressed as shown in the drawing. At this time, the brush I38 is in the position upon track I34 wherein it is twice as far from button I35 as it is from button I36. The stack damper I2 is two-thirds -closed with the motor mechanism I28 in this pof sition.

. voltage is approximately 20 volts.

upon energization of relay coil I52. The relay I5I includes a relay coil I56 and a cooperating armature I51 that controls a switch arm I58. Switch arm I58 is normally disengaged from a contact I59 but is moving into engagement therewith upon energization of relay coil I56.

The powdered fuel and air delivered to the boiler I from the duct 20 is adapted tobe ignited by an expanding pilot I65 which is connected to a main gas supply pipe I66 through an electrically operated valve I61. A by-pass pipe I68 serves to constantly permit a small flow of gas from the main gas supply pipe I66 to the pilot I65 so that a small flame is normally maintained at all times.

Upon energization of the gas valve I61, a large flow of gas is supplied to the pilot I65 whereupon its flame expands to the dotted proportions shown in the drawing as is usual in the art. The ignition valve I61 is controlled by a motor mechanism I10, which times the opening period of ignition valve I61, and by a relay Ill. The relay III includes a relay coil I12 and a cooperating armature I13 that controls a switch arm 114. The switch arm I14 is normally engaged with a contact I15 but moves from engagement therewith and into engagement with a contact I16- upon energization of relay coil I12. The motor mechanism I10 includes a main operating shaft I11 which is connected to a motor rotor I18 through suitable reduction gearing I19. The motor rotor I18 is provided with an energizingor field winding I80. The motor mechanism I10 also includes a rotary switching mechanism that comprises a Substantially circular track I8I and a pair of. contact buttons I82 and I83. This rotary switching mechanism further includes a brush I88 that is operated by the main operating shaft I11. Main operating shaft I11.also carries a cam I85 that is provided with a depressed portion I86 upon which a cam follower I81 rides. The cam follower I81 carries a mercury switch I 88, the arrangement being such that the mercury switch I88 is in open circuit position when the cam follower I81.is riding upon the depressed portion I86 of cam I85 and is in closed circuit position for all other positions of the cam I85. The motor mechanism I10 also includes a stepdown transformer I89 that comprises a high voltage primary I90 and a low voltage secondary I9I.

The control system further includes a pilot and burner flame responsive control system as well as a safety shut-down mechanism, this system and mechanism being shown enclosed by the dotted lines 200. This mechanism includes a combination transformer 20I and has a line voltage primary 202. This transformer 20I is provided with a high voltage secondary 203 of approximately 440 volts and a pair of series connected secondaries, or a center-tapped secondary, having secondaries or secondary portions 204 and 205. Each of these secondaries produces approximately 10- volts so that their combined The safety shut-down mechanism includes a thermally operated safety switch having contacts 206 and 201 which are normally latched in engagement with each other by a bimetallic element 208 which is adapted to be heated under certain conditions by an electrical heating element or safety switch heater 209. The arrangementis such that if the safety switch heater 209 is energized for a predetermined length of time, the free end of bimetallic element 208 unlatches safety switch contacts 206 and 201, allowing them to be separated after which they must be manually reclosed and will only be latched closed in the event that the bimetallic element 208 has cooled suflficiently.

This safety mechanism also includes a first relay having a coil 2I0 that controls an armature 2| I. The armature 2 is connected to a pair of switch arms 2I2 and 2I3 that are normally disengaged from their respective contacts 2I4 and 2I5 but are moved into engagement therewith upon energization of the relay coil 2I0. A second relay, which is included in the safety mechanism, includes a relay coil 2I6 and an armature 2I1. The armature 2" is connected to three switch arms 2I8, 2I9, and 220 which are normally in engagement with respective contacts 22!, 222, and 223. Upon energization of relay coil 2I6, these switch arms 2I8, 2I9 and 220 move from engagement with their contacts 22!, 222 v and 223 and the switch arms 2! and 220 move into engagement with contacts 224 and 225. The arrangement is such that switch arm 2 I8 engages contact 224 before it disengages contact 22I so that these contacts are overlappingly controlled. Associated with the relay coil 2I6 is a condenser 226. Direct current is furnished to the safety switch heater 209 and the relay coil 2I0 from one or both of low voltage secondaries 204 and 205 by means of a copper oxide disc rectifier of any well known construction having current paths 230, 23I, 232, and 233.

The flame responsive mechanism includes an electrode 235 which is adapted to be contacted by either the pilot flame when it is in its expanded condition or by the main flame issuing from the powdered coal burner. This electrode 235 is supported by a support partially shown at 236 and is connected to the grid 231 of a grid glow tube 238 by means of a wire 239. The grid glow tube 238 additionally includes the usual anode 240 and cathode 24I.

The safety mechanism and flame responsive mechanism can only be initially placed into operation if the stack damper I2 and'fuel control damper 2I have been moved to proper initial starting positions. To this end, the main operating shaft I2I of motor mechanism I is provided with a cam 250 that cooperates with a cam follower 25I which in turn carries a mercury switch 252. The arrangement is such that mercury switch 252 only closes when the motor mechanism I20 has operated the stack damper I2I to its full open position. Similarly, the main operating shaft 26 of motor mechanism 25 carries a cam 253 that operates a cam follower 254 which in turn carries a mercury switch 255. This arrangement is such that the mercury switch 255 is only closed when the fuel control damper 2I has been moved to some minimum fuel flow controlling position which may be varied from complete closed to some other desired minimum position by the manually operable rheostat I05 as will hereinafter be explained in detail. I

The motor I4 and various other of-the devices heretofore explained are controlled by a relay which includes a relay coil 251 and an armature 258. Armature 258 controls a pair of switch arms 259 and 260 that are normally disengaged from ,a pair of cooperating contacts 26I and 262. The switch arms 259 and 260 are moved into engagement with the contacts 26I and 262 upon energization of relay coil 251.

Operation of the whole system is dominated by a high limit pressure control 265 that is shown as comprising a bellows 266 which responds to. the pressure in boiler I and operates an arm 261 which is pivoted at 268. The arm 261 carries a mercury switch 269, the arrangement being such that mercury switch 269 is opened when the pressure in boiler I0 becomes excessive. The mercury switch 269 is interposed in a main line wire 210 which is connected to the hot line 5. In this manner, the main line wire 210 is only energized when the manual switch 1 is closed and when the boiler pressure is not excessive. The remaining circuit connections will be described in detail in the following detailed description of the operation of the complete system.

Operation With the parts in the position shown, the system is inoperative by reason of the fact that the manual main switch 1 is in open position. The boiler pressure is therefore quite low so that the mercury switch 269 of the high limit pressure controller 265 is closed and the control contact arm 54 is engaged with the extreme left hand end of control resistance 53. The fuel control damper 2| is completely, open and the mercury switch 255 is in open circuit position. The stack damper I2 is in two-thirds open position and the mercury switch 252 is also in open circuit posi-' tion. If the main switch 1 'is now closed, current will flow to the hot line 5 and also to the main line wire 210 since the mercury switch 269 is closed. Such closure of the main switch 1 results in energization of relay coil I56 by a circuit which goes from main line wire 210, a wire 215, relay coil I56 and wire 216 to ground 8. Energization of relay coil I56 moves switch arm I58 into engagement with contact I59 whereupon closure of main switch 1 also causes energization of field winding I33 of motor mechanism I20 as follows: hot line 5, wire 211, wire 218, wire 219, contact I55, switch arm I54, wire 280, track I34, brush I31, wire 28I and field winding I33 to ground 8. Main operating shaft I21 is thereupon rotated in a clockwise direction at relatively slow speed as viewed from the left. Crank I22 therefore lifts link I23 upwardly whereupon gear segment I 24 is rotated in a clockwise direction and the stack damper I2 is rotated in counterclockwise direction towards its full closed position. Brush I31 will also be rotated along track I34 away from button I35 and towards button I36. when brush I 31 rides off of track I34 and rests completely upon button I36, the energizing circuit for field winding I 33 will be interrupted.

At this time, the stack damper I2 will be com-- pletely closed. Engagement of brush I31 with button I36, however, establishes a new energizing circuit for field winding I33 as follows: hot line 5, wire 211, wire 335, switch, arm 90, contact 92,

wire 282, switch arm I58, contact I59, wire 283, 1

button I36, brush I31, wire 28I, field winding I33 and ground 8. The main operating shaft I2I therefore continues its clockwise movement. Brush I31 quickly rides off button I36 and back onto track I34 whereupon the field winding I33 remains energized by the circuit first described. Main operating shaft I3I therefore continues its clockwise rotation until brush I31 rides off track I34 and onto button I35 whereupon all circuits for field winding I 33 are interrupted. During this movement of the main operating shaft I2I while brush I31 moved from button I36 to button I35, the link I23 was moved downwardly whereby stack damper is rotated in a clockwise direction.

During this initial movement of main operating shaft I 2| the cam follower I40 was moved downwardly by cam I38 so as to engage contacts I42 and I43. With the parts in their new position, the stack damper I2 is completely opened and the mercury switch 252 has been moved to closed position.

Prior to closing of main switch 1, the fuel control damper 2| was in its full open position. It will be noted that with the main switch 1 open, solenoid winding 45 is substantially completely short circuited by the following circuit: wire I00, wire I02, switch arm 91, contact 99, wire I04, wire 11, wire 18, protective resistance 15 and wire 19. Solenoid winding 46 is likewise substantially completely short-circuited by the following circuit: wire I00, wire IOI, balancing contact finger 51, wire 8|, protective resistance 16 and wire 82. Since these protective resistances 15 and 16 are similar and of a like value, the solenoid windings 45 and 46, while both being substantially completely short circuited, are each energized slightly and to an equal extent so that plunger 41 is in the central position shown in the drawing wherein switch arm 48 is intermediate contacts 50 and 5I. Closure of main switch 1, together with closure of mercury switch 269, also caused energization of relay coil 95 of relay 86 by a circuit as follows: main line wire 210, wire 285, wire 286, wire 281, relay coil 95 and ground 8. Switch arm 91 thereupon moved out of engagement with contact 98so as to interrupt this substantial short circuit of solenoid winding 45. Movement of switch arm 91 into engagement with contact 99 however establishes a second substantially complete short circuit for solenoid winding 46 as follows: wire I00, wire I02, switch arm 91, contact 99, a wire 288, switch arm 89, contact 9I, wire I01, rheostat I05, wire I06, wire 80, wire 8I, protective resistance 16 and wire 82. Solenoid winding 46 therefore remains substantially completely short-circuited irrespective of the position of balancing contact finger 51 and solenoid winding 45 isno longer substantially completely short circuitedso that plunger 41 moves to the left and brings switch arm 48 into engagement with contact 50. Relay winding 31 is thereupon placed in parallel with a small number of turns of solenoid 45 and this full current flow goes through relay coil 38. This circuit is as follows: secondary 64, wire 69, wire 10, relay coil 38, at which point the circuit branches one portion going by way of relay coil 31, the wire 12 to wire H and secondary 64 1 'by energizing field winding 35 as follows: line 60, wire 65, relay switch arm 40, relay contact 43, wire 61, field winding 35, and wire 66 to line 6I. Motor rotor 33 is therefore rotated in a direction which results in rotation of main operating shaft 26 in a clockwise direction as viewed from the left. Fuel control damper 2I is thereby moved towards closed position and balancing contact finger 51 travels along balancing resistance 58 towards the left hand end thereof'a. When main operating shaft 26 has moved through a quarter revolution, balancing contact finger 51 engages the left hand end of balancing resistance 58 whereupon solenoid winding 45 is again substantially completely short-circuited. This circuit is as follows: wire I00, wire IOI, balancing contact finger 51, wire 18, protective resistance 15 and wire 19. Solenoid windings 45 and 46 now again both being substantially short circuited, the plunger 41 returns to its center position moving switch arm '48 from engagement with contact 50. This breaks the circuit through the small number of turns of solenoid 45 which was in parallel with relay coil 31 so that relay coils 31 and 38 are again equally energized, both being connected in series across the secondary 64. Plunger 39 therefore returns to its central position and moves relay switch arm 40 from engagement with relay contact 43 thereby deenergizing field winding 35. This quarter movement of main operating shaft 26 caused fuel control damper 2| to move to closed position and raised cam follower 254 so as to close mercury switch 255. At this time, it should be noted that by manual manipulation of rheostat I05, the short circuiting effect on solenoid winding 46 can be made less complete whereby balancing contact finger 51 will not move to the extreme left end of balancing resistance 58v in order to reb'alance the energization of solenoids 45 and 46. In this manner, the minimum flow position of fuel control damper 2I can be made less than completely closed if desired under these initial starting conditions.

Closure of manual switch 1, together with closure of mercury switch 269 also resulted in energization of primary 208 of transformer 20I by a circuit as follows: main line wire 210, wire 285, wire 286, primary 202 and ground 8. Therefore, as soon as both mercury switches 252 and 255 have been moved to'closed circuit position, which means that the stack draft I2 is completely open and fuel control damper 2I is completely closed, energizing circuits for relay coil 2I0 and safety switch heater 209 are established. During half of each cycle of the alternating current produced by the combined secondaries 204 and 205, the relay coil 2I0 and'the safety switch heater 209. in series, will be energized as follows: secondary 204, secondary 205, wire 289, wire 290, mercury switch 252, wire 29l, mercury switch 255, wire 292, switch arm 2I9, contact 222, wire 293, wire 294, safety switch contacts 206 and 201, wire 295, current path 230 of the rectifier, wire 296, relay coil 2I0, current path 23l of the rectifier, wire 291, switch arm 2l8, contact 22], wire 298, safety switch heater 209 and wire 299 to secondary 204. During the other half of each of the cycles of alternating current delivered by secondaries 204 and 205, the energizing circuit for relay coil H0 and safety switch heater 209 will be as follows: secondary 205, secondary 204, wire 299, safety switch heater 209, wire 298, contact 22I, switch arm 2I8, wire 291, current path 233 of the rectifier, wire 296, relay coil 2I0, current path 232 of the rectifier, wire 295, safety switch contacts 201 and'206, wire 294, wire 293, contact 222, switch arm 2I9, wire 292, mercury switch 255, wire 29l, mercury switch 252, wire 290 and wire 289 to secondary 205. Energization of relay coil 2I0, moves switch arms 2I2 and 2I3 into engagement with contacts 2I4 and 2 I5. Engagement of contact 2 by switch arm 2| 2 establishes holding circuits for relay coil 2| 0 and safety switch heater 209 which are entirely independent of mercury switches 252 and 255. During one half of each cycle of alternating current,

this holding circuit will be as follows: secondary 204, secondary 205, wire 289, wire 300, contact 2I4, switch arm 2I2, wire 30I, wire 294, safety switch contacts 206 and 201, wire 295, current path 230 of the rectifier, wire 296, relay coil 2I0, current path 23I of the rectifier, wire 291, switch arm 2I8,. contact 22I, wire 298, safety switch heater 209 and wire 299 to secondary 204. During the other half of each alternating cycle, the

holding circuit will be as follows: secondary 205,

secondary 204, wire 299, safety switch heater 209, wire 298, contact 22I, switch arm 2I8, wire 291, current path 233 of the rectifier, wire 296, relay coil 2I0, current path 232 of the rectifier, wire 295, safety switch contacts 201 and 206, wire 294, wire 30I, switch arm 2I2, contact 2I4, wire 300 and wire 289 to secondary 205. Energization of relay coil 2| 0 after it has initially been energized is therefore entirely independent of the mercury switches 252 and 255 so that the motor mechanisms I20 and I 25 may be thereafter operated in their proper manners as will soon be described without deenergizing the relay coil 2I0 and heater 209.

Movement of switch arm 2|3 into engagement with contact 2I5 establishes an energizing circuit for relay coil I12 as follows: main line wire 210, wire 285, wire 303, contact 2I5, switch arm 2I3, wire 304, wire 305, switch arm 220, contact 223, wire 206, relay coil I12 and ground 8. Energization of relay coil I12 moves switch arm I14 from engagement with contact I15 and into engagement with contacts I16. It will be noted that upon closure of main switch 1, transformer I 90 and field winding I in series were energized as follows: hot line 5, .wire 301, primary I90, wire 308, field winding I80, wire 309 and ground 8. However, withswitch arm I 14 in engagement with contact I15, the secondary I9I was open circuited, wherefore the current flow through primary I and field winding I80 was not sufiicient to operatively energize the field winding I80. Movement of switch arm I14 into engage- .ment with contact I16 completes an energizing upon rotated at slow speed in a counter-clock-.

wise direction as viewed from the left. Initial rotation of brush I 84 in counter-clockwise direction causes the same to engage track" I8I and leave button I83 whereupon a short circuit for secondary I9I is established which is independent of the contact button I83 and is independent of the switch arm I14 and contact I18. This new short circuit for secondary I9I is as follows: secondary I9I, wire 3I0, wire 3I4, track ondary I9I. Field winding I80 therefore remains energized until the main operating shaft I11 has completed a half cycle or of rotation whereupon brush I84 disengages track I8I and rests completely upon button I82. This movement is relatively slow and consumes a period of about 360 seconds. Initial counter-clockwise rotation I8I, brush I84 and wire '3I3 to the other side of sec-' ofmain operating shaft I11 causes the cam fol- I lower I81 to ride off of the depressed portion I86 of cam I85 whereupon mercury switch I88 is moved to closed circuit position thereby energizing ignition valve 161 as follows: main line wire 210, wire 285, wire 303, contact 215, switch arm 213, wire 304, wire 315, mercury switch 188, wire 316, ignition valve 161 and wire 311 to ground 8. If the pilot flame is out, so that it does not expand, the safety switch will open and render the system inoperative after the safety switch heater 209 has been energized for about 75 seconds. Energization of ignition valve 161 causes the same to open whereupon the pilot flame should expand to the proportions shown in dotted lines and impinge upon or contact the electrode 235. The charge on the grid 231 of grid glow tube 238 thereby drains off by way of wire 239, electrode 235 and the pilot flame whereupon current is permitted to flow from the anode to the cathode of the grid glow tube. A circuit is thereby established as follows: high voltage secondary 203, wire 318, anode 240, cathode 241, wire 319, wire 320, relay coil 216, wire 321 and wire 322 to the other side of secondary 203. ,It will be noted that the condenser 226- is connected in parallel with the relay coil 216 and thereby serves to smooth out the pulsating direct current which flows to the relay coil 216 from the secondary 203 and through the grid glow tube 238. Energization of relay coil 216 moves switch arm 218 into engagement with contact 224 and then out of engagement with contact 221, moves switch arm 219 from engagement with contact 222 and moves switch arm 220 from engagement with contact 223 and into engagement with contact 225. This disengagement of switch arm 218 from contact 221 interrupts the initial energizing and holding circuits for the safety switch heater 209 and relay coil 210 but engagement of switch arm 218 with contact 224 establishes maintaining circuits for relay coil 210 only as follows: during one half of each cycle from secondary 205, wire 289, wire 300, contact 214, switch arm 212, wire 301, wire 294, safety switch contacts 206 and 201, wire 295, current path 230, wire 296, relay coil 210, current path 231, wire 291, switch arm 218, contact 224 and wire 325 to secondary 205; and during the other half of each cycle from secondary 205, wire 325, con-, tact 224, switch arm 218, wire 291, current path 233, wire 296, relay coil 210, current path 232, wire 295, safety switch contacts 201 and 206, wire 294, wire 301, switch arm 212, contact 214, wire 300 and wire 298 to secondary 205. The safety switch heater 209 is thus deenergized. Movement of switch arm 220 from engagement with contact 223 interrupts the energizing circuit for relay coil 112 whereupon switch arm 114 returnsto the position shown in the drawing wherein it is disengaged from contact 116 and is engaged with contact 115. A short circuit for transformer 191 is thereupon established as follows as soon as brush 184 reaches button 182: transformer 191, wire 310, switch arm 114, contact 115, wire 326, contact button 182, brush 184 which is now engaging contact button 182 and wire 313 to secondary 191. Field winding will then be again energized and cause main operating shaft 111 to continue its counter-clockwise rotation. As soon as brush 184 engages track 181, a maintaining short circuit for secondary 191 is established as heretofore described. At this time, the cam follower 181 again rides upon the depressed portion 186 of cam so that mercury switch 188 again opens and the ignition valve 161 is deenergized. The main operating shaft 111 therefore completes another half revolution, bringing the parts to the 'position shown in the drawing wherein brush 184 engages contact button 183. As

pointed out before, this half revolution requires a period of time of about 360 seconds. Movement of switch arm 230 into engagement with contact 225 energizes relay coil 251 as follows: main line wire 210, wire 285, wire 303, contact 215, switch arm 213, wire 304, wire 305, switch arm 220, con-. tact 225, wire 321 and relay coil 251 to ground 8. Energization of relay coil 251 moves switch arms 259 and 260 into engagement with contacts 261 and 262. Engagement of switch arm 260 with contact 262 energizes pulverizer and blower motor 14 as follows: hot line 5, wire 328, contact 262, switch arm 260, wire 329, motor 14, wire 330 and ground 8. v Engagement of switch arm 259 with contact 260 energizes relay coils 81 and 152 as follows: main line wire 210, wire 331, contact 261, switch arm 259, wire 332, relay coil 81 to ground 8 and wire 333 to relay coil 152 and ground 8. Energization of relay coil 81 moves switch arm 89 from engagement with contact 91 and into engagement with contact 93. Movement of, switch arm 89 from contact 91 interrupts the short circuit for solenoid coil 46 and its movement into engagement with contact 93 connects the contact finger 54 with the balancing contact finger 51 and the junction of solenoid windings 45 and 46 whereby to place the pressure control potentiometer in control of the motor mechanism 25. The boiler pressure of course is low at this time inasmuch as the system has not been operating so that control contact finger 54 is engaging the extreme left hand of control resistance 53 whereby the solenoid winding 45 is substantially completely short-circuited as follows: solenoid winding 45, wire 100, wire 102, switch arm 91, contact 99, wire 228, switch arm 09, contact 93, wire 103, control contact finger 54, wire 11, wire 18, protective resistance 15 and wire 19 to the other end of solenoid winding 45. Plunger 41 therefore moves to the right and brings switch arm 48 into engagement with contact 51. A small number of turns of solenoid winding 46 is thereby placed in parallel with relay winding 38 the circuit being as follows: secondary 64, wire 11, wire 12, relay winding 31, at which point the circuit splits, one portion going by way of relay coil 38 and wire 10 to wire 69 and secondary 64, whereas the other portion goes by way of wire 109, protective resistance 108, wire 110, switch arm 48, contact 51, wire 112, the small number of turns of solenoid winding 46, and wire 13 to wire 69 and the same side of secondary 64. In this manner, relay winding 31 becomes more highly energized than relay winding 38, whereupon switch arm 40 moves into engagement with relay contact 42 and energizes field winding 36 as follows: line 60, wire 65, relay switch arm 40, relay contact 42, field winding 36 and wire 66 to line 61. The rotor 34 therefore rotates main operating shaft 26 in a counter-clockwise direction as viewed from the left. This counter-clockwise rotation of main operating shaft 26 continues until the parts return to the position shown in the drawing wherein balancing contact finger 51 engages the extreme right hand end of balancing resistance 158 whereby it substantially short circuits the solenoid winding 46 thereby rendering the energizations of the solenoid windings 45 and 46 equal as heretofore explained. The fuel control damper 21 is therefore moved to full open position and into the duct 20 and into the boiler 10 as heretofore pointed out. Energization of relay coil 81 also moved switch arm 90 from engagement with contact 92 and moved the same into engagement with contact 94. Field winding I33 of motor mechanism I20 was thereupon energized as follows: hot line 5, wire 211, wire 335, switch arm 90, contact 94, wire 336, contact button I35 which is now engaged by brush I31, brush I31 and wire 28I to field winding I33 and ground 8. The main operating shaft I2I is thereby rotated in a clock- 10 wise direction and the link I23 is moved upward- 1y until the stack damper I2 is returned to its two-thirds closed position. At that time, brush I31 will be returned to the position shown in the drawing and cam follower I40 will move upwardly to move contact I42 from engagement with contact I33. Field winding I33 will thereupon be deenergized and the draft damper I2 will remain in its two-thirds closed position. This partially closed position of the damper I2 varies with different boilers and the proper adjustment for a particular installation can be obtained by properly positioning the cam I38 on the main operating shaft I2 I. During this time, the fuel delivered to the boiler should be ignited by the expanded pilot flame. If ignition properly takes place, then when the pilot flame is contracted by the operation of the motor mechanism I10 in the manner just described,the electrode 235 will be contacted by the main burner flame so as to maintain relay coil 2I6 energized and the safety switch heater 209 deenergized. If flame should not be established at the main burner, contracting of the pilot will result in movement of the pilot flame away from the electrode 233 whereupon a charge will build up on the grid 231 and block the passage of current through the grid glow tube 238 resulting in deenergization of relay coil 2I6. Safety switch heater 209 will thus be reenergized as soon as motor mechanism I10 starts through its second half revolution and will cause the bimetallic element 208 to open the safety switch contacts in about 75 seconds, which is less than the time required by the motor mechanism to complete such half-revolution. The system is thereby rendered inoperative until manual intervention.

With the system operating normally, as the boiler temperature increases, control contact finger 54 will move across control resistance 53 towards the right hand end thereof. Such movement of the control finger 54 causes the shortcircuiting of solenoid coil 45 to be less complete and when the voltage drop across solenoid coil 45 becomes greater than that across solenoid coil 46, the plunger 41 will move to the left bringing contact arm 48 into engagement with contact 50 whereupon plunger 39 will also move to the left to energize field winding 35 as previously pointed out. Main operating shaft 26 will therefore ro- 60 tate in a clockwise direction moving balancing contact finger 51 along balancing resistance 58 until the voltage drops across solenoid windings 45 and 46 are again equalized. The opposite action takes place on a fall in boiler pressure.

Therefore, during normal operation, the position of the fuel control damper 2| is modulated or proportioned in a well known manner to main-.

tain the boiler pressure within prescribed limitsto which the range of movement of the pressure operated potentiometer responds. For a more detailed description of this proportioning or modulating action from a control potentiometenreference may be had to the copending application 75 of Lewis L. Cunningham, Ser. No. 673,236 entitled Remote stator sy temflsnd yfilediivrs The rheostat 105, has -beenipreyiously set so that the fuel control-damper2l cannot becompletely closed whereby toprovidea minimum operating condition. Itmayhappenthat the loadon the boiler is so small that this minimum operating condition or minimum fuel feed causes the boiler pressure to'become excessive whereupon bellows 266 will expand, lifting .arm 261.: and tilting mercury switch 269 to open circuit position. When this happens, the energizing circuits for relay coil I56, for the transformer 20I, for relay 251 and for relay I1I will all be interrupted if they have not already been interrupted during normal operation. Deenergization of relay coil 251 results in deenergization of motor I4 and also causes deenergization of relay coils 81 and I52. The parts therefore all assume the position shown in Fig. 1 of the drawing and upon a subsequent reclosure of mercury switch 269, due to a subsequent decrease in boiler pressure, the apparatus will go through the starting cycle previously explained after which control will be returned to the potentiometer pressure controller.

In the event of a failure of flame during normal operation, relay coil 2I6 will be deenergized due to the absence of flame and the system will be rendered inoperative until manual intervention. if there should be a failure of electrical power during normal operation, the system will completely recycle and go through the starting operations in the manner previously explained.

To recapitulate, with the power off, the parts assume the position shown in the drawing wherein the draft damper is two-thirds closed and the fuel supply is completely open. However, the fuel feeding and draft producing motor is deenergized. Upon closure of the power circuit by manual manipulation of manual switch 1, relay coil I58 is energized, power is supplied to transformer 20I, and power is supplied to transformer I89 and relay coil 95 is energized. Energization of relay coil I56 causes the motor mechanism I20 to run to the position in which the stack damper I2 is fully opened and in which the mercury switch 252 is closed. Energization of relay coil 95 operates the motor mechanism 25 to move fuel control damper 2| to its minimum position and closes mercury switch 255. Closure of mercury switches 252 and 255 energizes relay coil 2I0 which then establishes its own holding circuit independent of these mercury switches and energizes relay I12 that in turn opens the ignition valve and maintains it open fora timed period through the motor mechanism I10. Immediately upon opening of the ignition valve, the relay coil 2| 0 is energized whereupon relay coil 251 is energized and starts the motor. This energization of relay coil 251 also energizes relay'coils I52 and 81 whereupon the control of the motor mechanism 25 is turned over to the potentiometer controller responsive to pressure conditions and the motor mechanism I20 is operated to positionthestack damper I2 in two-thirds closed position. If flame is not produced, deenergization of the ignition means causes deenergization Iofrelay coil 2-I6 whereupon the motor mechanism I20 begins its return to initial position and the safety switch heater is reenergized and causes the safety. switch to open during this returnmovement of motor mechanism I10. In this .m'annenfthe system locks up until manual intervention. If, o the other hand, combustion is properly established, the relay coil 2 I6 is maintained energized and the system is in normal operation. The supply of fuel and air is thereafter modulated or proportioned in accordance with fluctuations in boiler pressure. If the boiler pressure should become too high by reason of a small load, the system is shut down and thereafter goes through the above described sequence when the boiler pressure returns to a desired safe value. If there should be a failure of flame during normal operation, relay coil 2I0 becomes deenergized and the system will be rendered inoperative until manual intervention.

It will be evident that many changes in the system of the present invention can be made without departing from the spirit thereof and I therefore intend to be limited only by the scope of the appended claims.

I claim:

1. A burner system of the class described, comprising in combination, fuel control means in control of the supply of fuel to a burner, draft control means for the burner having a starting and a running position, a control operative to position the draft control means in starting position upon an initial demand for the feeding of fuel, means operative to institute the feeding of fuel by said fuel control means only after said draft control means has been positioned in starting position, ignition means for the fuel, and means responsive to the ignition means operative to thereafter position said draft control means in running position.

2. In a burner control system, in combination, fuel control means in control of the supply of fuel to a burner, a damper associated with the burner and having a starting position and a running position, a control operative to position the damper in its starting position upon an initial' demand for the feeding of fuel to the burner, means operative to initiate the supplying of fuel to the burner only after the damper has been moved to its starting position, means to ignite the fuel and means operated as a result of the feeding of fuel operative to move the damper to T its running position and maintain the same therein including means responsive to combustion of the fuel.

3. In combination, a burner, means in control of the flow of fuel to the burner, a control device responsive to the demand for heat associated with said means and operative to vary the supply of fuel to the burner according to such demands, draft control means having a starting position and at least one running position, a limiting control responsive to a heat condition operative to place said draft control means in its starting position upon the heat condition falling to a predetermined value, means operative to place the fuel control means under the control of said control device only after the draft control means reaches its starting position, and means for placing said draft control means in running position after it has been placed in its starting position.

4. In combination with a burner, draft control means having a starting and a running position, limiting control means responsive to a heat condition operative to place the draft control means in starting position upon the heat condition falling to a predetermined value, switching means moved to a new circuit controlling position when the draft control means reaches its starting position, electrically operated fuel control means in control of the supply of fuel to the burner, a circuit operative to place said fuel control means in operation completed by said switching means when moved to said new circuit controlling position, circuit connections operative to maintain said fuel control means in operation after the same has been initially placed in operation, and means operative to place the draft control means in running position after it has been placed in its starting position.

5. In a burner control system, a control device responsive to the demands for heat, fuel control means normally positioned by said control device to vary the supply of fuel in a plurality of stages upon fluctuations in the demand for heat, a limiting control responsive to a heat condition, fuel delivery means, connections between said limiting control, fuel delivery means and fuel control means operative to stop the supplying of fuel and to position the fuel control means in maximum fuel delivery position when the limiting control is in a first position as a result of an increase in the value of said heat condition and to position the fuel control means in minimum flow position when the limiting control is in a second position as' a result of a subsequent lowering of the value of said heat condition, connections between the fuel control means and fuel delivery means operative to place the fuel delivery means in operation only after the fuel control means has been placed in its minimum fuel control position, and means operative to thereafter maintain the fuel delivery means in operation until the limiting control again moves to its first position.

6. In combination, a burner, fuel delivery means, means in control of the volume of fuel delivered to the burner by the fuel delivery means, a heat condition responsive limiting control arranged to prevent operation of the fuel delivery means and to position the fuel volume control means. in maximum fuel flow position when the main control is in one positionas a result of an increase in the heat condition to which it responds and to position the fuel volume control means in minimum fuel flow position when in a second position as a result of a subsequent decrease in such heat condition, a second means to its minimum fuel flow position as a.-

result of movement of the limiting control from its first position to its second position and means operative to thereafter maintain operation of the fuel delivery means until the limiting control returns to said first position.

'7. In combination, a burner, fuel delivery means, means in control of the volume of fuel delivered to the burner by the fuel delivery means, draft control means having a starting and a running position, a heat condition responsive limiting control operative to' place the fuel volume control means in minimum fuel fiow position and the draft control means in starting position when the limiting control moves from a first position in response to an excessive heat condition to a second position in response to a decrease in said heat condition, means controlled by the conjoint action of the draft control means and fuel volume control means to place the fuel delivery means in operation only after the draft control means moves to starting position and the fuel volume control means moves to minimum fuel flow position, a second control operative to position the fuel volume control means in a plurality of positions, means to ignite the fuel, and

means responsive to ignition of the fuel operative to maintain operation of the fuel delivery means, place the draft controlling means in running position and place the fuel volume control means under the control of said second control.

8. In combination, a burner, fuel delivery means for delivering fuel to the burner, fuel volume control means in control of the volume of fuel delivered to the burner by the fuel delivery means, a heat condition responsive limiting control having first and second controlling positions, means controlled by the limiting control to place the fuel volume control means in minimum fuel flow position upon movement of the main control from its first position to its second position as a result of decrease of said heat condition below an excessive value, ignition, means, means controlled by the fuel volume control means operative to place the ignition means in operation only after the fuel volume control means reaches its minimum fuel fiow position, a second control operative to position the fuel volume control means in a plurality of positions, means responsive to proper operation of the ignition means operative to place the fuel delivery means in operation and to place the second control in control of the fuel volume control means, means to terminate operation of the ignition means, and means to maintain operation of the fuel delivery means and to maintain the second control in control of the fuel volume control means until the main control returns to its first position after the ignition means is rendered inoperative.

9. In combination, a burner, fuel delivery means for delivering fuel to the burner, fuel volume control means in control of the volume of fuel delivered to the burner by the fuel delivery means, draft control means having starting and running positions, a heat condition responsive limiting control having first and second controlling positions, means controlled by the limiting control to place the draft control means in starting position and the fuel volume control means in minimum fuel flow position upon movement of the limiting control from its first position to its second position as a result of a decrease in said heat condition, ignition means, means controlled by the draft control means and fuel volume control means operative to place the ignition means in operation only after the draft control means 55 reaches its starting position and the fuel volume control means reaches its minimiun fuel flow position, a second control operative to position the fuel volume control means in a plurality of positions, means responsive to proper operation of the ignition means operative to place the draft control means in running position, to place the fuel delivery means in operation and to place the second control in control of the fuel volume control means, means to terminate operation of the 65 ignition means, and means responsive to combustion conditions to maintain the draft control means in running position, to maintain operation of the fuel delivery means and to maintain the second control in control of the fuel volume con- 70 trol means until the limiting control returns to its first position after the ignition means is rendered inoperative. 10. In combination, a burner, fuel delivery means for delivering fuel to the burner, fuel 75 volume control means in control of the volume of fuel delivered to the burner by the fuel delivery means, a heat condition responsive limiting control having first and second controlling positions, means controlled by the limiting control to place the fuel volume control means in minimum fuel flow position upon movement of the limiting control from its first position to its second position upon a decrease in said heat condition below an excessive value, ignition means, means controlled by the fuel volume control means operative to place the ignition means in operation only after the fuel volume control means reaches its minimum fuel flow position, a second control operative to position the fuel volume control means in a plurality of positions, means responsive to proper operation of the ignition means operative to place the fuel delivery means in operation and to place the second control in control of the fuel volume control means, means to terminate operation of the ignition means, and means to maintain operation of the fuel delivery means and to maintain the second control in control of the fuel volume control means until the limiting control returns to its first position after the ignition means is rendered inoperative, said means responding to combustion conditions.

11. A burner control system, comprising in combination, means in control of the flow of fuel to the burner, a control associated with the fuel control means and operative to position the same in a plurality of fuel flow positions upon changes in the demand for fuel, ignition means, means operative to place the ignition means in operation for a time period upon an initial demand for fuel feed, and a single mechanism responsive to the proper operation of the ignition means and the successful establishment of combustion operative to. initially permit and to thereafter con-.

tinue the supplying of fuel to the burner.

12. A burner control system, comprising in combination, means in control of the flow of fuel to a burner, a control associated with the fuel control means and operative to position the same in a plurality of fuel flow positions upon changes in the demand for fuel, a flame producing ignition means, means operative to place the ignition meansin operation for a time period upon an initial demand for heat, and a single flame responsive device responsive both to the ignition flame and the burner flame operative to permit initiation of the supply of fuel to the burner if the ignition flame is properly established and to continue the feeding of fuel after termination of the ignition flame if combustion has been successfully established.

13. In combination with a furnace, a combination fuel pulverizer and feeding mechanism, a motor for driving the same, a fuel control valve in control of the volume of fuel delivered by said combination fuel pulverizer and feeding mechanism, a furnace stack damper having starting and running positions, a first control having first and'second control positions, means controlled by the first control and operative to position the stack damper in starting position and to position the fuel control valve in its minimum fuel control position when the first control moves from its first control position to its second control position, a second control for variably positioning the fuel control valve, connections by which the second control is placed in command of the fuel control valve and said motor is operated only after the stack damper has been moved to its starting position and the fuel conposition.

14. In combination with a furnace, a combination fuel pulverizer and feeding mechanism, a

10 motor for driving the same, a fuel control valve in control of the volume of fuel delivered by said combination fuel pulverizer and feeding mechanism, a furnace stack damper having starting and running positions, a first control having first l5 and second control positions, means controlled by the first control and operative to position the stack damper in starting position and to position the control valve in its minimum fuel control position when the first control moves from its first control position to its second fuel control position, a second control for variably positioning the fuel control valve, connections by which the second control is placed in command of the fuel control valve and said motor is operated only after the stack damper has been moved to its starting position and the fuel control valve has been moved to its minimum fuel flow position, and means responsive to the establishment of combustion operative to place the stack damper in running position, maintain operation of said motor and maintain said second control in control of the fuel control valve after said stack damper moves to its running position.

15. In combination, a burner, a draft control means, fuel feed control means, a first control,

connections by which the first control places the draft control means in starting position upon a call for heat, ignition means, connections by which the ignition means and fuel feed control means are placed in operation only after the draft control means reaches starting position and means responsive to the successful establishment of combustion operative to move the draft control means out of starting position and to maintain operation of the fuel feed control means after the draft control means has been so moved.

16. In combination, a burner, a draft control means, fuel feed control means, a first control, connections by which the first control places the draft control means in starting position upon a call for heat, ignition means, connections by which the ignition means and fuel feed control means are placed in operation only after the draft control means moves to starting position, means responsive to proper operation of the ignition means to place the draft control means in running position, and means to terminate operation of the ignition means, said ignition responsive means also responding to the burner flame to maintain operation of the fuel feed control means after the ignition means is rendered inoperative and the draft control means has been moved to running position.

17. In combination with a burner, a ;draft damper, control means for moving said damper to a wide open position, switching means moved to a new circuit controlling position when the draft damper reaches its wide open position, electrically operated fuel control means in control of the supply of fuel to the burner, a circuit operative to place the fuel control means in operation completed by said switching means when moved to said new circuit controlling position, circuit connections to maintain said fuel control means in operation after the same has been initially placed in operation, and means operative to move the damper away from its wide open position.

18. In a control system for a furnace having a draft damper and a fuel feeding means, control means responsive to heat conditions operative to move the draft damper to a wide open position when the heat condition falls to a predetermined value, means operative to place the fuel feeding means in operation when the draft damper reaches the wide open position, means for maintaining the fuel feeding means in operation even though the draft damper is subsequently moved away from its wide open position, and means for subsequently moving the draft damper away from its wide open position.

19. In a control system for a furnace having a draft damper and a fuel feeding means, control means for moving the draft damper to a wide open position, means for placing the fuel feeding means in operation when the draft damper reaches a wide open position, means for igniting the fuel supplied by the fuel feeding means, and means operative upon the successful establishment of combustion for moving the draft damper away from the wide open position.

20. In a control system fora furnace having a draft damper and a fuel feeding means, control means for moving the draft damper to a wide open position, means for placing the fuel feeding means in operation when the draft damper reaches a wide open position, means for igniting the fuel supplied by the fuel feeding means,

means operative upon the successful establishment of combustion for moving the draft damper away from the wide open position, and means for maintaining the fuel feeding means in operation even though the draft damper is moved away from the wide open position.

LEON L. KUEMPEL. 

